This proposal addresses basic research on baculovirus host range and virulence to multiple insect complexes. A restricted host range, unstable virulence and poor growth in cell culture have restricted the commercial acceptance and production of baculoviruses as biological pesticides. For these reasons, baculoviruses are currently used on a limited basis in controlling insect pests on economically important food and fiber resources. However, baculoviruses are highly virulent to their specific host insect. Furthermore, the EPA has registered several baculoviruses for commercial application to insect pests on agricultural commodities. The baculoviruses of Spodoptera frugiperda (fall armyworm) SfMNPV and Autographa californica (alfafa looper) AcMNPV, which are pathogenic to insects of agricultural importance, will be studied by biochemical and genetic analysis because they grow in cell culture, they have overlapping hosts, and they have regions of DNA sequences in common. The proposed study will analyze virulence and host range determinants of these viruses by genetic recombination of temperature-sensitive AcMNPV mutants with SfMNPV, and by cotransfection of AcMNPV and SfMNPV genome and cloned DNAs. The origin of the recombinant sequences and the location of recombination sites will be determined by DNA restriction enzyme analysis, physical mapping, and DNA-DNA blot hybridization of cloned and uncloned DNA from parental and progeny viruses that have recombined. The host range and virulence of recombinant baculoviruses and the parental viruses will be compared in insect cell cultures and in larvae. The expansion of the insect host range of baculoviruses and the increase in virulence to insects will reduce the production costs of these biological pesticides. Implementation of these baculovirus recombinants as either short or long term control agents can be expected to reduce the amounts of chemical pesticides currently being used to manage insect pest populations. Such reductions would be advantageous from both the standpoint of human health and environmental safety aspects.